The major objective is to investigate synaptic mechanisms of action of major anticonvulsant drugs and some convulsant drugs using the frog neuromuscular junction as a convenient, appropriate paradigm of a synapse. This preparation will be used to investigate the possible synaptic effects of the anticonvulsant drugs, phenytoin, phenobarbital and ethosuximide as well as convulsant drugs such as pentylenetetrazol, penicillin and the barbiturate CHEB. These will be studied using conventional stimulation and intracellular recording techniques. The amplitude and frequency of miniature end-plate potentials, the amplitude of end-plate potentials and the muscle membrane resistance will be estimated in normal Ringer's solution. Quantal content in partially curarized preparations will be determined by the coefficient of variation method. In media in which quantal release has been reduced or in preparations in which contraction has been disrupted, quantal content will be calculated as the ratio between mean end-plate potential and miniature end-plate potential amplitudes. The response to trains of stimuli in the presence of these agents will also be assayed. By contrasting the effects of anticonvulsants with differing spectra of clinical usefulness, and comparing these with the effects of antagonistic convulsant agents, differences in the manner in which these substances affect synaptic transmission will be demonstrated which could lead to a significant classification of properties.